Loop holding mechanism for use in a multi-axial yarn structure forming machine

ABSTRACT

In a loop holding mechanism (31), loop engaging pins (39) which are carried by pin blocks (38) are arranged successively to engage at a feed end (310) of the mechanism loop portions of yarns formed at opposite side edges of a multi-axial yarn structure being formed. The pin blocks (38) at each side of the mechanism (31) advance in abutting relationship along an advancement track (32) to a delivery end (311) of the mechanism (31) where they are returned along a return track (34) and again engaged in the successively formed loop portions. The pin blocks (38) are biased by biasing devices (48, 53) into abutting engagement with each other in the advancement track (32) to provide accurate control of the spacing between the pins (39) engaging the loop portions and are advanced along the advancement track (32) by a drive pinion which engages in turn each pin block (38) advanced to it to move the engaged pin block (38) an all the pin blocks (38) in the advancement track (32) in the direction of the delivery end (311) of the mechanism.

BACKGROUND OF THE INVENTION

The present invention relates to a loop holding mechanism for holdingand engaging loop portions of yarns successively produced at oppositeside edges of a multi-axial yarn structure being formed and a machinefor forming a multi-axial yarn structure.

It has been proposed to provide a machine for producing multi-axial yarnstructures in which warp yarns are supplied in a warp feed direction inthe form of a warp sheet and in which a yarn transfer device is providedwhich subjects warp yarns to successive bias yarn forming steps in whicheach yarn is caused to move in a succession of lateral transfer steps ina first weft direction to move from a first bias yarn reversal positionto a second bias yarn reversal position and then to move in a successionof return lateral transfer steps in the opposite direction from thesecond bias yarn reversal position to the first bias yarn reversalposition thereby to form a non-woven bias yarn assembly comprising twosuperposed non-woven bias yarn sub-assemblies in which the bias yarns ofone sub-assembly are inclined to the bias yarns of the othersub-assembly and in both of which the bias yarns are inclined to thewarp feed direction and in which each bias yarn at each reversalposition in proceeding from a transfer step in one direction to atransfer step in the opposite direction forms a bias yarn loop portion.

In publication EP 0263392-A2 there is disclosed a machine for forming atwo dimensional tetra-axial woven yarn structure embodying warp yarns,weft yarns and a bias yarn assembly having two bias yarn sub-assembliesin which the bias yarns of each are inclined to the bias yarns of theother and to the warp and weft yarns. The machine includes a yarntransfer device for progressively transferring yarns fed to it toprovide the sub-assemblies of oppositely inclined bias yarns and in oneform of yarn structure produced, the bias yarn sub-assemblies arearranged between outer warp yarns and outer weft yarns and the warpyarns are woven with the weft yarns to hold the intermediate bias yarnsin place in the fabric.

The weaving together of the outer warp yarns and outer weft yarns in themachine disclosed in EP 0263392-A2 serves to hold the intermediate biasyarns in place in the structure and tensions in the bias yarns arisingfrom their displacement by the traversing device are adequately absorbedin the woven structure thus formed.

In WIPO publication No. WO92/14876 a method of forming athree-dimensional woven yarn structure is disclosed in which use is madeof a yarn transfer device for transferring yarns in the weft directionto provide bias yarn arrays in which the yarns are inclined to the warpfeed direction and in which the arrays of inclined bias yarns are woveninto other arrays of yarns by selective shedding of the yarns andinsertion of weft yarns to produce the three-dimensional structure.

Again, the weaving of the arrays of bias yarns with other arrays ofyarns and the insertion of weft yarns in the method disclosed inWO92/14876 allows the tensions in the bias yarns to be absorbed.

In U.S. Pat. No. 5,137,058 there is disclosed a machine for forming athree-dimensional yarn structure embodying warp yarns, weft yarns andnon-woven bias yarns which are held together by binding warp yarns whichpass through the yarn structure between adjacent non-binding warp yarns.The machine includes a yarn transfer device for progressivelytransferring yarns fed to it to provide non-woven sub-assemblies ofoppositely inclined bias yarns which are fed into a binding zone wherethey are held in place within the warp and weft yarn structure by thebinding warp yarns. The binding warp yarns are held captive at the upperand lower faces of the yarn structure by weft yarns inserted at eachface. In addition, the bias yarns of the bias yarn sub-assemblies areheld in place at their yarn reversal positions along each edge of thestructure being formed by an outer binding warp yarn which passesthrough the bias yarn loop portions formed at the yarn reversalpositions.

While the machine disclosed in U.S. Pat. No. 5,137,058 produces athree-dimensional yarn structure in which the non-woven bias yarnsub-assemblies are held in place by the binding warp yarns which passthrough the structure and by the outer binding warp yarns, the yarnstructure produced by the machine would have a tendency to reduce inwidth as a result of the tensions built up in the bias yarns of the biasyarn sub-assemblies.

In WIPO publication WO94/16131 a method of forming a multi-axial yarnstructure is disclosed in which the two non-woven bias yarnsub-assemblies are formed in a yarn transfer device in which each yarnis caused in a succession of lateral transfer steps to follow the yarnpreceding it from one position to another position in a lateral transferpath extending in the weft direction until the yarn has moved from afirst bias yarn reversal position to a second bias yarn reversalposition and then in a succession of return lateral transfer steps inthe opposite direction and along the same transfer path until the yarnarrives at the first yarn reversal position. The lateral transfer stepsand the return transfer steps are then successively repeated. The needto provide for a supply of yarns to the device from a rotary supply suchas a rotary creel as required in the machine of U.S. Pat. No. 5,137,058is by this mode of yarn transfer in the transfer device obviated.

The yarn structures produced in the method disclosed in WO94/16131includes the two bias yarn sub-assemblies formed by the yarn transferdevice and additionally includes binding warp yarns which pass throughthe bias yarn sub-assemblies and which are held captive at the lower orupper face or at the lower and upper faces of the yarn structure byinsertion of weft yarns.

While the yarn transfer device disclosed in WO94/16131 has the advantagethat it obviates the need for a rotary yarn supply, for example in theform of a rotary annular creel, there remains the disadvantage that thebinding warp yarns which serve to hold the yarns of the bias yarnsub-assemblies in place in the structure may not in some circumstancesadequately prevent the yarn structure being formed from reducing inwidth under the tensions developed in the bias yarns of the two biasyarn sub-assemblies.

In European patent publication No. 0573132-A1 there is disclosed amachine for producing a three-dimensional woven yarn structure in whichweft yarns are arranged in columns which extend from one face of thestructure to an opposite face and are interlocked by warp yarns whichextend through the structure from a first of the two faces of thestructure along an inclined path to the opposite face of the structureand then along a return inclined path back to the first face of thestructure to produce what is known as an angle interlock woven yarnstructure. In addition, selvedge forming warp yarns are woven into thestructure so as to successively pass from one face to the other and backthrough the structure between adjacent columns of weft yarns.

In the machine disclosed in EP 0573132-A1 the yarn structure isdescribed as being formed in the machine with the width direction of thestructure extending vertically and with the inclined bias yarns and theselvedge forming warp yarns extending between upper and lower faces ofthe structure being formed. Selvedge holding mechanisms are describedfor engaging the loop portions of the selvedge forming warp yarns at theupper and lower faces of the yarn structure to prevent a reduction inthe width of the woven structure being formed due to tension produced inthe warp yarns and with the aim of maintaining the width (height) of thewoven structure constant.

In a first of the selvedge holding mechanisms disclosed in EP0573132-A1, there is provided an arrangement of four guide rails whichextend in the direction in which the woven yarn structure is deliveredfrom the weaving zone of the machine. Two of the guide rails extendalong the length of the upper face of the woven structure at oppositeupper edges of the structure and the other two guide rails extend alongthe length of the lower face of the structure also at opposite loweredges of the structure. Each of the rails provides for the support of amultiplicity of roller hook elements and a holding bar is passed througheach loop portion of the selvedge forming warp yarn at each of the upperand lower faces of the woven structure, where it is hooked at each endon hooks of the roller hook elements which are caused to enter into andengage in the two guide rails at that face. When the woven yarnstructure reaches a discharge end of the selvedge holding mechanism theroller hook elements disengage from the guide rails and subsequently theholding bar which they have supported is removed manually orautomatically from the loop portions of the selvedge forming warp yarnsand then inserted manually or automatically into the loop portions ofselvedge forming warp yarns at the entry end of the guide rails whereroller hook elements are provided for supporting the bar.

In an alternative selvedge holding mechanism disclosed in EP 0573132-A2the roller hook elements and the guide rails supporting them arereplaced by pin blocks which are guided in guide rails and which carrypins which are arranged to engage in the loop portions of the selvedgeforming warp yarns at the upper and lower faces of the yarn structurebeing formed. There is however no disclosure as to how the pins arebrought into engagement with the loop portions and as to how they arefed into the entry ends of the guide rails, removed from the exit endsof the rails and then returned to the entry ends of the rails and thepins again engaged in further loop portions of the selvedge forming warpyarn.

While the selvedge holding mechanisms disclosed in EP 0573132-A1 providea means by which the woven structure being formed can be prevented fromreducing in width, there is no disclosure of a means by which this canbe achieved automatically and with a precision necessary for thereliable production of non-woven and partially non-woven multi-axialyarn structures.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a loop holdingmechanism for holding and engaging loop portions of yarns successivelyproduced at opposite side edges of a multi-axial yarn structure beingformed and a machine embodying the loop holding mechanism for forming amulti-axial yarn structure in which a non-woven bias yarn assembly isformed comprising two superposed non-woven bias yarn sub-assemblies inwhich the bias yarns of one sub-assembly are inclined to the bias yarnsof the other sub-assembly and in both of which the bias yarns areinclined to the warp feed direction and in which the loop holdingmechanism serves to reduce or eliminate the adverse effects of tensionin the yarns of the bias yarn sub-assemblies in the formed multi-axialyarn structure by engagement and disengagement of loop portions of thebias yarns in a precise and reliable manner.

According to a first aspect of the present invention there is provided:

a loop holding mechanism for engaging and holding loop portions of yarnssuccessively formed at first and second edges of a multi-axial yarnstructure being formed, the loop holding mechanism comprising:

(a) a plurality of pin blocks each of which carries a loop engaging pin,

(b) first and second pin block advancement tracks in which the pinblocks are advanced from first and second pin insertion stations tofirst and second pin retraction stations spaced from the first andsecond pin engaging stations in the direction in which the formedmulti-axial yarn structure is to be advanced,

(c) first and second pin block return tracks in which pin blocks arereturned from the first and second pin retraction stations to the firstand second pin insertion stations,

(d) first and second pin-block insertion means at the first and secondpin insertion stations successively to transfer pin blocks from thereturn tracks to the advancement tracks for insertion of pins of the pinblocks in loop portions successively formed at the pin insertionstations,

(e) first and second pin-block retraction means at the first and secondpin retraction stations to transfer the pin blocks from the first andsecond advancement tracks to the first and second return tracks therebysuccessively to retract pins of the pin blocks from the loop portions atthe pin retraction stations,

(f) advancement track pin block biasing means to bias the pin blocks ineach of the pin block advancement tracks into abutting engagement witheach other, and

(g) a drive mechanism at a drive station in each of the advancementtracks to engage in turn each pin block advanced thereto under the biasof the biasing means to drive the engaged pin block and all the pinblocks in the advancement track between the drive station and the pinretraction station along the pin advancement track in the direction ofthe pin retraction station against the action of the biasing means tobring a pin block into the pin retraction station and to permit all pinblocks in the track between the drive station and the pin insertionstation to advance in the advancement track under the bias of thebiasing means to bring a pin block out of the pin insertion station andinto the pin block advancement track and to advance a pin block into thedrive station.

In an embodiment of the invention hereinafter to be described:

(a) the drive station in each of the advancement tracks is located a t aposition along the track intermediate the pin insertion station and thepin retraction station and

(b) the advancement track pin block biasing means comprises:

(i) forwardly acting biasing means located at the pin insertion stationin each advancement track to bias the pin blocks between the pininsertion station and the drive station in the direction of the drivestation and into abutment with each other and

(ii) rearwardly acting biasing means located at the pin retractionstation to bias the pin blocks between the drive station and the pinretraction station in the direction of the drive station and intoabutment with each other.

In an embodiment of the invention hereinafter to be described:

(a) the drive mechanism at the drive station of each pin-blockadvancement track comprises a drive pinion located at the drive stationand provided with equi-spaced peripheral teeth and

(b) each pin block carries a tooth element which is engagable at thedrive station by a peripheral tooth on the pinion for advancement of thepin block along the pin block advancement track upon rotary movement ofthe pinion.

In the embodiment of the invention hereinafter to be described:

(a) each pin insertion station includes a pin block insertion guidetrack extending between an exit end of the pin block return track and anentry end of the pin block advancement track and

(b) the pin block insertion means provides for displacing a pin block ata pin block delivery position in the pin block insertion track at theexit end of the pin block return track to a pin insertion position inthe pin block insertion track at the entry end of the pin blockadvancement track to insert the pin of the pin block in the yarn loopportion at the station and for entry of the pin block into the pin blockadvancement track.

In the embodiment of the invention hereinafter to be described:

(a) each pin retraction station extends between an exit end of the pinblock advancement track and an entry end of the pin block return trackand

(b) the pin block retraction means provides for displacing a pin blockat a pin block retraction position in the pin retraction station at theexit end of the pin block advancement track to retract the pin of thepin block from the yarn loop portion and to deliver the pin block to apin block return position in the pin retraction station at the entry endof the pin block return track for entry into the pin block return track.

In the embodiment of the invention hereinafter to be described, a returntrack pin-block biasing means is provided at the entry end of the pinblock return track to bias the pin block at the pin block returnposition and all the pin blocks in the pin block return track intoabutting relationship for movement in the return track in the directionof the pin insertion station and each pin block arriving at the exit endof the return track is delivered to the pin block delivery position inthe pin insertion station under the action of the return-track pin-blockbiasing means.

In the embodiment of the invention hereinafter to be described:

(a) the first pin block return track is arranged parallel to and abovethe first pin block advancement track,

(b) the second pin block return track is arranged parallel to and abovethe second pin block advancement track, and

(c) the pin block retraction means at each pin retraction stationcomprises a lifting device which engages the pin block at the pin blockretraction position and lifts it to the pin block return position.

In an embodiment of the invention hereinafter to be described, thelifting device comprises a displaceable member carrying retractablesupport means which ride over the pin block in a downward excursion ofthe lifting device and engage under the pin block or a part or partsthereof to support the pin block during a return excursion of thelifting device, whereby the pin block is lifted to the pin block returnposition. The lifting device comprises a displaceable arm and theretractable support means takes the form of one or more spring biasedpawls.

In an embodiment of the invention hereinafter to be described the pinblock advancement and return tracks are arranged to provide forhorizontal movement of the pin blocks and the pin insertion tracks andthe pin block retraction means are arranged to provide for movement ofthe pin blocks vertically during insertion of pins of the pin blocksinto the loop portions of the yarn structure being formed and duringretraction of the pins of the pin blocks at the pin block retractionstations.

According to a second aspect of the present invention there is provideda machine for forming a multi-axial yarn structure comprising loopholding means according to the first aspect of the invention wherein:

(a) warp yarns are supplied in a warp feed direction in the form of awarp sheet and

(b) a yarn transfer device is provided which subjects warp yarns tosuccessive bias yarn forming steps in which each yarn is caused to movein a succession of lateral transfer steps in a first weft direction froma first bias yarn reversal position to a second bias yarn reversalposition and then to move in a succession of return lateral transfersteps in the opposite direction from the second bias yarn reversalposition to the first bias yarn reversal position thereby to form anon-woven bias yarn assembly comprising two superposed non-woven biasyarn sub-assemblies in which

(i) the bias yarns of one sub-assembly are inclined to the bias yarns ofthe other sub-assembly,

(ii) the bias yarns are inclined to the warp feed direction and

(iii) the bias yarns at each bias yarn reversal position in proceedingfrom a transfer step in one direction to a transfer step in the oppositedirection form bias yarn loop portions at the first and second edges ofthe structure being formed.

While the yarn traversing device may take a variety of different forms,the yarn transfer device may advantageously be such that each yarn iscaused in a succession of lateral transfer steps to follow the yarnpreceding it from one position to another position in a lateral transferpath extending in the weft direction until the yarn has moved from thefirst bias yarn reversal position to the second bias yarn reversalposition and then in a succession of return lateral transfer steps inthe opposite direction and along the same transfer path until the yarnarrives at the first yarn reversal position.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 is a schematic isometric view of a simple three-dimensional yarnstructure which can be produced on the multi-axial yarn structureforming machine according to the invention and as illustrated in FIG.2A.

FIG. 2A is a block schematic diagram of a multi-axial yarn structureforming machine according to a first embodiment of the invention.

FIG. 2B is a schematic diagram of a yarn transfer mechanism of themachine shown in FIG. 2A.

FIG. 3 is a schematic sectional side elevation of a loop portion holdingmechanism for use in the machine as shown in FIG. 2A, the section beingtaken on the line III--III in FIG. 4.

FIG. 4 is a schematic plan view of the loop portion holding mechanismshown in FIG. 3.

FIG. 5 is a part sectional end view of the loop portion holdingmechanism shown in FIG. 3, viewed in the direction in which the formedyarn structure is fed to the mechanism.

FIG. 6 is a schematic part sectional end view of the mechanismillustrated in FIG. 3 viewed in the direction in which the formed yarnstructure is delivered from the mechanism and showing pin blockretraction devices in raised dispositions.

FIG. 7 is a schematic end view corresponding the end view shown in FIG.6, except insofar that the pin block retraction devices are shown inlowered dispositions.

FIG. 8 is a part-sectional side elevation of a part of the mechanismillustrated in FIG. 3, showing a drive mechanism for advancement of pinblocks in pin block advancement tracks of the mechanism.

FIG. 9 is a schematic side elevation of the feed end of a loop portionholding mechanism for the machine shown in FIG. 2A in accordance with asecond embodiment of the invention and showing to an enlarged scale analternative pin block biasing structure at the feed end,

FIG. 10 is a schematic end view of the part of the loop portion holdingmechanism shown in FIG. 9,

FIG. 11 is a schematic part sectional side elevation of the delivery endof a loop portion holding mechanism for the machine shown in FIG. 2A andshowing to an enlarged scale an alternative biasing structure forbiasing pin blocks at the delivery end of the mechanism as well as pinblocks of an alternative form to the pin blocks illustrated in FIGS. 3to 8,

FIG. 12 is a schematic part sectional side elevation of the feed end ofthe loop portion holding mechanism of the machine shown in FIG. 2,illustrating pin blocks of the alternative form and alternative biasingstructure for the pin blocks at the feed end,

FIG. 13 is a sectional plan view of the feed end of the mechanism shownin FIG. 12, taken on the line XIII--XIII in FIG. 12 with parts cut awayto reveal some detail below the section line,

FIG. 14 is a schematic part sectional side elevation of the feed end ofthe loop portion holding mechanism shown in FIG. 12, except insofar asthe pin block at the feed end of the mechanism is shown displaced to alowered disposition where it is engaged by the alternative biasingstructure, and

FIG. 15 is a schematic part sectional plan view of the feed end of themechanism shown in FIG. 12 with the pin block displaced to the lowereddisposition illustrated in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a simple form of three-dimensional yarnstructure is shown which can be produced on the multi-axial yarnstructure forming machine to be described with reference to FIGS. 2A and2B and FIGS. 3 to 8 and which comprises a non-woven warp yarn assemblycomposed of two superposed non-woven diagonal sub-assemblies of warpyarns 11 and 12 arranged at angles of ±45° to the reference warpdirection R, a binding warp yarn assembly comprising binding warp yarns13 extending in the warp feed direction and passing through thenon-woven diagonal warp yarn sub-assemblies 11 and 12, an upper weftyarn assembly comprising weft yarns 14 and a lower weft yarn assemblycomprising weft yarns 15.

A multi-axial yarn structure forming machine is illustrated in outlinein FIG. 2A for forming the yarn structure of FIG. 1 and comprises acreel 16 which supplies warp yarns in a warp sheet 17 in a warp feeddirection F to a yarn transfer mechanism 18 following passage throughyarn support elements 19 of a jacquard mechanism 20. Each warp yarn ofthe warp sheet 17 is supported by its own yarn support element 19 whichcan be raised and lowered under the control of the mechanism 20 to formsheds in which warp yarns of the warp sheet 17 are raised. Suchmechanisms are well known in the art and can be used for making complexselections for the shedding of the warp sheet in the formation offabrics of intricate pattern. The mechanism provided in the machineillustrated in FIG. 2A is employed also for raising and lowering warpyarns of the warp sheet 17 during yarn transfer carried out by the yarntransfer mechanism 18.

The yarn transfer mechanism 18 shown more clearly in FIG. 2B comprises alower yarn guide member 21 which extends in the weft directionthroughout the width of the warp sheet 17 and includes upstanding yarnguide elements 26 which (i) extend through the thickness of the warpsheet 17, (ii) define warp yarn guide openings 27 through which the warpyarns of the warp sheet 17 pass and (iii) hold the warp yarns inpredetermined positions spaced apart in the weft direction and a warpyarn transfer member 22 which also extends in the we ft direction andwhich includes spaced yarn guide elements 28 defining transfer openings29 for the reception of yarns of the warp sheet 17 for transfer in theweft direction to produce the bias warp yarns 11 and 12 which are toform part of the yarn structure produced on the machine.

The yarn transfer mechanism 18 in the machine illustrated in FIGS. 2Aand 2B subjects the warp yarns of the warp sheet 17 to successive biasyarn forming steps in which each yarn is caused to move in a successionof lateral transfer steps in a first weft direction from a first biasyarn reversal position to a second bias yarn reversal position and thento move in a succession of return lateral transfer steps in the oppositedirection from the second bias yarn reversal position to the first biasyarn reversal position thereby to form two superposed non-woven biasyarn sub-assemblies as shown in FIG. 1, the bias yarns 11 of onesub-assembly being inclined to the bias yarns 12 of the othersub-assembly and at ±45° to the warp feed direction. Transfer of thebias yarns 11 and 12 by the transfer mechanism 18 is fully described inInternational Application PCT/GB94/00028 Publication WO94/16131. In theformation of the two non-woven sub-assemblies each bias yarn at eachyarn reversal position in proceeding from a transfer step in onedirection to a transfer step in the opposite direction forms as shown inFIG. 1 bias yarn loop portions 101 and 102 at opposite edges of thestructure 10.

The machine shown in FIG. 2A also includes a weft insertion station 23for inserting the weft yarns 14 of the structure shown in FIG. 1 and abinding warp yarn insertion mechanism 25 which includes an insertionneedle 26 which provides for the insertion of the binding warp yarns 13of the structure 10 shown in FIG. 1. It also includes a beater 30.

The yarn structure shown in FIG. 1 is formed from the two non-woveninclined bias yarns 11 and 12, the binding warp yarns and the upper andlower weft yarns 14 and 15 in a succession of processing steps in acycle of operation following each transfer step of the yarns 11 and 12in the yarn transfer mechanism 18. Following a bias yarn transfer stepin the mechanism 18 a binding warp yarn insertion step is carried out inwhich binding warp yarn is passed through the bias yarn structure behindthe bias yarns 11 and 12 by the insertion needle 26 followed by a weftinsertion step in which a lower weft yarn is inserted at the weftinsertion station 23 behind the binding warp yarn. This is followed by abeating up step using the beater 30 to bring the bias yarns 11 and 12and the newly inserted lower weft yarn 15 to the fell point of the yarnstructure being formed. The beater 30 is then retracted and the bindingwarp yarn needle 26 is returned to its retracted position followingwhich a further weft yarn insertion step is carried out by insertion ofan upper weft yarn behind the return run of the binding warp yarn and isfollowed by a further beating up step. The beater 30 is then returned toits retracted position to complete the steps in a complete cycle ofoperation of the machine which is then repeated by the commencement ofthe next yarn transfer step carried out by the transfer mechanism 18.

As is schematically illustrated in FIG. 2A the yarn structure 10 thusformed is delivered to a loop portion holding mechanism 31 now to bedescribed with reference to FIGS. 3 to 8.

Referring now to FIGS. 3 and 4, and more particularly to FIG. 3, themechanism 31 includes a feed end 310 to which the formed yarn structure10 is fed in the direction F and a delivery end 311 from which the yarnstructure 10 is delivered for further processing. The yarn structure 10is in a manner hereinafter to be described advanced from the feed end310 to the delivery end 311 under the control of pin blocks 38 which arearranged to advance in abutting relationship to each other along a pinblock advancement track provided at each side of the mechanism 31 in amode of operation in which pin blocks 38 at the feed end 310 arearranged successively to move down and into the pin block advancementtracks to bring the depending pins 39 thereon into yarn loop portions101 and 102 at opposite side edges of the structure 10 and to advancewith the structure 10 along the advancement tracks in the feed directionF, following which the pin blocks 38 are raised at the delivery end 311to disengage the pins 39 from the yarn structure 10 and are moved into apin block return track provided along each side of the mechanism formovement therein in a direction opposite to the feed direction F forsubsequent further engagement of their pins 39 with the loop portions101 and 102 at the feed end 310 of the mechanism. One pin blockadvancement track 32 is shown in FIG. 3, partly cut away to reveal thepin blocks 38 for advancement in the track and one pin block returntrack 34 is also shown partly cut away to reveal the pin blocks 38arranged therein for return movement along the track.

Referring now to FIG. 5, which is an end view of the mechanism 31showing the feed end 310 to which the formed yarn structure 10 is fed,the mechanism 31 includes the pin block advancement track 32 at one sideof the mechanism and the further pin block advancement track 33 at theother side of the mechanism and the pin block return track 34 on the oneside of the mechanism and the further pin block return track 35 on theother side of the mechanism. Each of the tracks 32 to 35 is providedwith support structure 36 and 37 which serve to support for slidingmovement therealong the pin blocks 38 carrying depending pins 39. Thebeater 30 is shown with upstanding beater pins 301.

At the feed end 310 of the machine, as shown in FIG. 5, the advancementand return tracks 32 and 34 terminate at a pin block insertion station40 and the advancement and return tracks 33 and 35 terminate at afurther pin block insertion station 41. Each of the pin block insertionstations 40 and 41 includes a pin block guide track structure 42 bywhich a pin block 38 on leaving the return track and taking up apin-block delivery position in the guide track structure is guided to apin insertion position at the entry end of the advancement track and apneumatically operated plunger 43 is provided at each pin insertionstation 40, 41 for engaging the pin block 38 at the pin-block deliveryposition and delivering it to the pin insertion position at the entryend of the advancement track.

Pin blocks 38 are advanced along the pin block advancement tracks 32 and33 from the feed end 310 of the machine shown in FIG. 5 to the deliveryend 311 of the machine shown in FIGS. 6 and 7 and are then returnedalong the pin block return tracks 34 and 35.

At the delivery end 311 of the mechanism 31 as illustrated in FIGS. 6and 7, the pin block advancement track 32 and the associated pin blockreturn track (not shown) terminate at a pin retraction station andsimilarly the pin block advancement track 33 and the associated pinblock return track (not shown) terminate at a further pin retractionstation 45. Each of the retraction stations 44 and 45 includes a liftingdevice 47 which is arranged to engage a pin block 38 on leaving the pinblock advancement track and on taking up a pin block retraction positionand lift it to a pin block return position at the entry end of the pinblock return track.

Referring again to FIGS. 3 and 4 the pin blocks 38 in the advancementtrack 32 are held in abutting relationship in the track 32 by aforwardly acting biasing structure 48 including a biasing spring 49acting on a yoke member 50 fixedly mounted on a shaft 51 which carries acranked biasing arm 52, the free end of which is arranged to bearagainst the pin block 38 at the entry end of the advancement track 32thereby to bias the pin block and those in advance of it in theadvancement track 32 into abutment with each other and in the directionof the delivery end 311 of the mechanism 31. The shaft 51 of the pinblock biasing structure 48 is arranged to carry a further crankedbiasing arm for biasing the pin blocks in the other advancement track 33into abutting engagement with each other and in the direction of thedelivery end 311. At the delivery end 311 a further biasing structure 53is provided which comprises a pneumatic cylinder 54 secured at one endby a pivot pin 55 to the mechanism frame and carrying a biasing pistonacting on a piston rod 56 to apply through a linkage 57 secured to ashaft 58 a biasing force on an arm 59, the free end of which exerts arearwardly acting force on the pin block 38 at the exit end of theadvancement track 32 and all the pin blocks 38 in the track 32 inopposition to the forwardly acting biasing force of the biasingstructure 48 thereby to maintain the blocks 38 in abutting relationshipto each other. The shaft 58 also carries a further biasing arm forbiasing the pin blocks 38 in the advancement track 33 rearwardly intoabutting engagement with each other and in the direction of the feed end310.

The pin blocks 38 in the pin block return track 34 are urged in toabutting relation and in the direction of the feed end 310 of themechanism 31 by a further biasing structure 60 which comprises apneumatic cylinder 61 pivotally secured to the frame of the mechanism 31by a pivot pin 62 and carrying a biasing piston acting on a piston rod63 to apply through a link 64 secured to a shaft 65 a rearwardly actingbiasing force on a biasing lever 66 which is secured to the shaft 65 andthe free end of which bears on the pin block 38 at the entry end of thereturn track 34 urging engaged pin block 38 and all the pin blocks 38 inthe return track 34 into abutting relationship with each other and inthe direction of the feed end 310 of the mechanism 31. The biasing ofthe pin blocks 38 in the pin block return track 35 is provided by afurther arm mounted on the shaft 65.

Referring now to FIG. 8, this is a plan view drawn to an enlarged scaleof the feed end 310 of the mechanism 31 in the region of the pin blockadvancement and return tracks 33 and 35. Parts of the mechanism havebeen cut away to reveal pin blocks 38 in the pin block advancement track33 which are arranged to be advanced in the track in the direction ofthe delivery end 311 of the mechanism 31 under the control of a drivemechanism 67. As will be seen, each pin block 38 carries a laterallyextending tooth 68, the disposition of which is best illustrated in FIG.5 and the drive mechanism comprises a pinion 69 carrying peripheralequi-spaced teeth 70 which upon rotation of the pinion 69 on a driveshaft 71 successively engage the tooth 68 on each pin block 38 in turnto advance it in the advancement track 33 against the biasing action ofthe pin block biasing structure 53. Advancement by the pinion 69 of thepin blocks 38 between the pinion and the exit end of the track 33 isaccompanied by advancement of the pin blocks 38 between the pinion 69and the feed end 310 of the mechanism under the forward biasing actionof the pin block biasing structure 48. The drive shaft 71 is driventhrough a gear box 72 having an input shaft 73 driven through a chaindrive 74 from a drive shaft 75, which also serves to provide a drive asshown in FIG. 4 for a drive mechanism 76 for advancing the pin blocks 38in the pin block advancement track 32. As will be seen in FIGS. 3 and 4the drive shaft 75 carries a sprocket 77 secured thereto which is drivenby a chain drive 78 in turn driven by a principal machine drivecontrolling the take-off movements of the yarn structure forming machineillustrated in FIG. 2A.

The loop portion holding mechanism 31 as described is arranged tocomplete successive cycles of operation, each of which in the embodimentherein described commences following a bias yarn transfer step by theyarn transfer mechanism 18, a binding warp yarn insertion step, a weftinsertion step and a beating up step using the beater 30 which bringsthe bias yarns 11 and 12 and the newly inserted lower weft yarn 15 tothe fell point of the yarn structure being formed. The beater 30 is soarranged as to bring the loop portions 101 and 102 of the bias yarns 11and 12 of the newly formed structure into position in the yarn insertionstations 40 and 41 and a complete cycle of operation of the mechanism 31then follows.

To simplify description of the operation of the mechanism 31, referencewill be made to movement of pin blocks 38 in the advancement and returntracks on one side only of the mechanism and it is to be understood thatpin blocks 38 in the tracks on the other side of the mechanism will movein unison therewith.

Prior to commencement of a cycle of operation of the mechanism 31 a pinblock 38 occupies the pin block delivery position at the exit end of thereturn track with the actuating plunger 43 in its raised position and apin block 38 occupies at the exit end of each of the advancement tracksthe pin-block retraction position in which it is engaged by the liftingdevice 47 and the actuator 79 is in the lowered position as shown inFIG. 7.

The cycle of operation of the mechanism 31 commences with the pin block38 in the pin-block delivery position at the exit end of the returntrack being caused to move downwardly under the action of the actuatingplunger 43 to the pin insertion position at the entry end of theadvancement track thereby to cause pins 39 of the pin blocks 38 toengage in the loop portions 101 and 102 positioned at the pin insertionstation.

During movement of the pin block 38 to the pin insertion position thebiasing arm 52 is moved against the action of its biasing force to allowpassage of the pin block 38, which upon arrival at the pin insertionposition, is then biased by the arm 52 into abutting relation with theother pin blocks within the advancement track.

The lifting devices 47 (FIGS. 6 and 7) are then raised by retraction ofthe actuator 79 to bring the pin blocks 38 at the pin-block retractionpositions at the exit ends of the advancement tracks 32 and 33 to thepin-block return positions at the entry ends of the return tracks 34 and35, during which movement the biasing arms 66 of the biasing structure60 are displaced by the pin blocks 38 and then take up dispositionsbiasing the raised pin blocks 38 into the entry ends of the returntracks 34 and 35.

Each insertion plunger 43 is then retracted to its retracted positionshown in FIG. 5 and the pin blocks 38 in the return tracks 34 and 35 areurged by the biasing structure 60 along the return tracks to bring theforemost of the pin blocks 38 into the pin-block delivery position atthe exit end of each of the return tracks and the pin block at the pinblock return position in each of the pin retraction stations 44 and 45into the entry end of the return track.

The lifting devices 47 at each of the pin retraction stations 44 and 45are then lowered under the action of the pneumatic actuator 79 from theposition shown in FIG. 6 to the position shown in FIG. 7.

Lowering of the lifting devices 47 is then followed by other weavingfunctions and by movement of the pinion 69 of each of the two drivemechanisms 67 and 76 to advance the pin blocks 38 in the advancementtracks 32 and 33 to bring the foremost of the pin blocks 38 into the pinblock retraction stations 44 and 45.

Advancement of the pin blocks 38 along the advancement tracks 32 and 33completes the cycle of operation which is then repeated by operation ofthe plungers 43 at the pin insertion stations 40 and 41, which bring thepin blocks 38 delivered to the pin insertion stations from the pin-blockdelivery positions at the exit ends of the return tracks and into thepin insertion positions following the next beating up operation of thebias yarns as previously described.

Support for the pin blocks 38 in the lifting devices 47 is, as shown inFIG. 7, provided by a spring biased pawl 471 which is carried at the endof a leaf spring 472 and which engages under an abutment face on the pinblock 38 and a further spring biased pawl of the same form as the pawl471 which is carried by a spring 473 and which engages under the tooth68 in the pin block 38.

In the embodiment of the invention hereinbefore described, the steps inthe cycle of operation of the mechanism 31 are such that the liftingdevices 47 are lowered before movement of the foremost of the pin blocks38 into the pin block retraction positions at the exit ends of theadvancement tracks 32 and 33 under the action of the pinions 69.

In an alternative embodiment of the invention these steps are reversedand the pin blocks 38 advanced by the pinions 69 to bring the foremostof the pin blocks 38 into the pin retraction positions at the pin blockretraction stations and the lifting devices 47 are then lowered from theposition shown in FIG. 6 to the position shown in FIG. 7. During thismovement the spring biased pawl 471 rides over the pin block 38 at thepin retraction position and engages under the abutment face on the pinblock 38 and the further spring biased pawl carried by the spring 473rides over the tooth 68 on the pin block 38 and engages under it.

The yarn structure of FIG. 1 is of simple form and the yarn structureforming machine illustrated in FIG. 2A for forming it is also of thesimplest form. It will however be appreciated that in many practicalapplications the yarn structures will need to be of considerably morecomplex form and include for example additional superposed non-wovensub-assemblies of bias yarns positioned on the yarn structure above orbelow the non-woven sub-assemblies of bias yarns 11 and 12 and formed inthe same manner as the sub-assemblies of bias yarns 11 and 12 and inaddition to the binding warp yarns 13 additional warp yarns which extendin the reference warp direction R and which are either non woven orwoven with weft yarns 15 or additional weft yarns. Furthermore, the yarnstructure being formed may be one in which the binding warp yarns do notpass through the entire thickness of the structure, but pass round aweft yarn at an intermediate depth of the structure and further bindingwarp yarns employed to extend through the structure from the oppositedirection to the intermediate depth where they pass round a weft yarn sothat the structure finally produced can be folded back to produce forexample a T-section structure.

While each warp yarn of the warp sheet 17 as described with reference toFIG. 2A is supported by its own yarn support element 19, it will beappreciated that in the weaving of some yarn structures it may beconvenient to route several yarns through one yarn support element 19.

Furthermore, while the mechanism 20 provided in the machine illustratedin FIG. 2A is employed simply for raising and lowering warp yarns of thewarp sheet 17 during yarn transfer carried out by the yarn transfermechanism 18, it will be appreciated that the mechanism can withadvantage be used for weaving layers of warp yarns with weft yarns.

The yarn transfer mechanism 18 described with reference to FIGS. 2A and2B takes the form of a lower yarn guide member 21 having upstanding yarnguide elements defining yarn guide openings through which the yarns ofthe warp sheet 17 pass and a warp yarn transfer member 22 which includesspaced yarn guide elements defining transfer openings for the receptionof yarns of the warp sheet 17 for transfer to other openings in thelower yarn guide member 21. In order to avoid contact of the yarns withthe guide elements in their transfer between the yarn guide member 21and the yarn transfer member 22, use may be made of eyelet elementsthrough which the yarns of the warp sheet 17 pass and which aresupported by the guide elements for sliding movement therealong into andout of the yarn guide openings and the yarn transfer openings asdisclosed in and forming the subject of co-pending UK patent applicationNo. 9416721.0 (International patent application publication No.WO96/06213).

In the yarn structure of FIG. 1 as produced by the machine illustratedin FIG. 2A, the bias yarns 11 and 12 are formed as two superposednon-woven bias yarn sub-assemblies in which the bias yarns 11 of onesub-assembly are inclined to the bias yarns 12 of the other sub-assemblyand at ±45° to the warp feed direction. It will however be appreciatedthat by an appropriate modification to the operation of the transfermechanism 18 the bias yarns 11 and 12 can be arranged to be inclined toeach other and to the warp feed direction at angles other than ±45°.

In the yarn structure of FIG. 1 as produced by the machine illustratedin FIG. 2A the binding warp yarns are secured by upper and lower weftyarns 14 and 15. It will however be appreciated that for some purposesit may be desirable or preferable to arrange that the binding warp yarnsare secured by passing round the bias yarns 11 and 12.

While advancement of the pin blocks 38 in the advancement tracks isachieved by a drive mechanism including chain drives 74, it will beappreciated that alternative drives, for example, worm drives couldalternatively be used.

The yarn structure forming machine illustrated in FIG. 2A is describedas carrying out a bias yarn transfer step, a binding warp yarn insertionstep, a weft insertion step and a beating up step in bringing thecomponents of the structure to the yarn insertion stations 40 and 41. Itwill however be appreciated that these steps may be augmented byadditional steps in the formation of more complex yarn structures andthe order of the steps varied.

It will be appreciated that the pin block biasing structures 48, 53 and60 for maintaining the pin block 38 in abutting relationship as well asthe pin blocks 38 themselves as described with reference to FIGS. 3 to 8may take alternative forms, for example, as now to be described withreference to FIGS. 9 to 15.

In particular, the forwardly acting biasing structure 48 of FIG. 3 bywhich the pin blocks 38 in the advancement tracks 32 are biasedforwardly in the track into abutting relationship with each other may bereplaced by the alternative biasing structure 148 illustrated in FIGS. 9and 10 in which a pneumatic cylinder 149 replaces the spring 49. As willbe seen, the cylinder 149 is secured at one end by a pivot pin 150 tosupport structure 151 of the mechanism frame and carries a biasingpiston acting on a piston rod 152 to apply through a linkage 153 abiasing force on an arm 154 fixedly mounted on a rotatable support shaft155 upon which is also fixedly mounted a cranked arm 156 which replacesthe cranked biasing arm 52 of the biasing structure illustrated in FIG.3.

It will be seen that the biasing structure 148 serves only to provide abiasing force on the advancement track on one side of the mechanism 31.An additional biasing structure not shown identical to the structure 148is provided for applying a biasing force to the pin block 38 in theadvancement track on the other side of the mechanism. It will however beappreciated that for some applications it may be found desirable oradvantageous to employ a single biasing structure 148 as shown in FIGS.9 and 10 and so to extend the shaft 155 as to enable it to carry acranked arm 156 at each end for applying the appropriate biasing forceto the pin blocks 38 in both advancement tracks.

The biasing structure 53 of the mechanism 31 described with referencesto FIGS. 3 to 8 for exerting a rearwardly acting force on the pin block38 at the exit end 311 of each of the advancement tracks 32 and 33 aswell as the biasing structure 60 for biasing the pin blocks 38 into thepin block return tracks 34 and 35 may be replaced by an alternativebiasing structure 153 now to be described with reference to FIG. 11.

As will be seen from FIG. 11, pin blocks 381 in the pin blockadvancement track 32 and the pin block return track 34 on one side ofthe machine are biased at the delivery end 311 of the mechanism 31 inthe direction of the feed end of the mechanism by an arm 254 whichcarries pin block engaging parts 255 and 256 and which is pivotallymounted by a pin 257 in a yolk member 258 carried by a piston rod 259 towhich a biasing thrust is applied by a pneumatic cylinder 260. A furtherbiasing structure identical to the structure 253 is provided at theother side of the mechanism at the delivery end 311 to provide for thebiasing of the pin blocks 381 in the pin block advancement track 33 andthe pin block return track 35.

The use in the embodiment described with reference to FIGS. 3 and 4 ofthe numerous shafts and linkages provided with the pneumatic cylinders54 and 61 for exerting the biasing forces on the pin blocks 38 at thedelivery end is thus conveniently replaced by the simplified arrangementof biasing arms 254 of the two biasing structures 253 in the arrangementillustrated in FIG. 11.

It will be seen that the pin block 381 illustrated in FIG. 11 takes analternative form to that of the pin block 38 of the embodiment describedwith reference to FIGS. 3 to 8. In particular, and as best seen in FIGS.12 and 13, depending pins 39 of the pin blocks 381 are secured to a noseportion 382 which extends from the rear face 383 of each pin block. Whenin abutting relationship with other pin blocks in the advancement andreturn tracks the nose portion 382 of each pin block 381 engages in acomplementary recess 384 in the front face 385 of the next adjacent pinblock, as best seen in FIG. 13. Such relocation of the pin 39 enablesthe pin at the feed end 310 of the mechanism 31 to protrude between thebeater pins 301 of the beater 30 and obviates the need to activate orcrank a beater pin 301 around the pin block as illustrated in FIG. 5.

It will furthermore be seen from FIG. 13 that the pin block 381 includesa tooth profile 386 of full form which replaces the half tooth profile68 of the pin block 38 shown in FIG. 8.

It will of course be appreciated that the pin blocks may take any one ofa variety of different forms depending upon the conditions under whichthey are required to operate.

It will also be seen that in the embodiment illustrated in FIGS. 12 and13 a biasing arm 201 is provided for biasing the pin blocks 381 into theadvancement track on each side of the machine and that it takes a formdifferent from that of the cranked arm 52 of the FIG. 3 embodiment andthe cranked arm 156 of the FIG. 9 embodiment. The arm 201 in particularincludes a pin block engaging rib 202 of such dimensions as to enable itto pass into the space between adjacent pins 301 of the beater 30 as nowto be described with reference to FIGS. 14 and 15.

It will be seen that in FIGS. 12 and 13 a pin block 381 has taken up adelivery position at the end of the pin block return track 34 ready fordisplacement to the pin insertion position at the entry end of the pinblock advancement track 32. In the manner hereinbefore described thispin block 381 is displaced by the actuator 43 to the pin insertionposition as illustrated in FIG. 14. During this movement it displacesthe biasing arm 201, with the rib 202 being brought to bear on the rearface 383 of the pin block 381 when the pin block 381 takes up the pininsertion position at the entrance to the pin block advancement track32. As will be seen from FIG. 15 the rib 202 of the arm 201 passesthrough the space between two adjacent pins 301 of the beater 30 or onthe outside of the final beater pin 301 thereby obviating the need tocrank one of the beater pins 301 as illustrated in FIG. 5.

In the yarn structure forming machine described with reference to FIGS.2A and 2B, the yarn transfer mechanism 18 comprises the lower yarn guidemember 21 and the yarn transfer member 22 which subjects the warp yarnsof the warp sheet 17 to the succession of bias yarn forming steps inwhich each yarn is caused to move in a succession of lateral transfersteps first in one direction and then in the opposite direction toproduce the inclined sub-assemblies of bias yarns 11 and 12. Ashereinbefore described, the loop portion holding mechanism 31 isarranged to complete successive cycles of operation, each of whichcommences following a bias yarn transfer step by the yarn transfermechanism 18, a binding warp yarn insertion step, a weft insertion stepand a beating up step using the beater 30 which brings the bias yarns 11and 12 and the newly inserted weft yarns to the fell point of the yarnstructure being formed. The loop portions 101 and 102 of the bias yarns11 and 12 of the newly formed structure are brought into position in thepin insertion stations 40 and 41 of the mechanism 31 and a completecycle of operation of the mechanism 31 then follows.

What is claimed is:
 1. A loop holding mechanism (31) for engaging andholding loop portions of yarns successively formed at first and secondedges of a multi-axial yarn structure being formed, the loop holdingmechanism (31) comprising:(a) a plurality of pin blocks (38) each ofwhich carries a loop engaging pin (39), and (b) first and second pinblock advancement tracks (32, 33) in which the pin blocks (38) areadvanced from first and second pin insertion stations (40, 41) to firstand second pin retraction stations (44, 45) spaced from the first andsecond pin insertion stations (40, 41) in the direction in which theformed multi-axial yarn structure is to be advanced,characterised by thefact that the loop holding mechanism (31) further comprises: (c) firstand second pin block return tracks (34, 35) in which pin blocks (38) arereturned from the first and second pin retraction stations (44, 45) tothe first and second pin insertion stations (40, 41), (d) first andsecond pin-block insertion means (43) at the first and second pininsertion stations (40, 41) successively to transfer pin blocks (38)from the return tracks (34, 35) to the advancement tracks (32, 33) forinsertion of pins (39) of the pin blocks (38) in loop portions (101,102) successively formed at the pin insertion stations (40, 41), (e)first and second pin-block retraction means (47) at the first and secondpin retraction stations (44, 45) to transfer the pin blocks (38) fromthe first and second advancement tracks (32, 33) to the first and secondreturn tracks (34, 35) thereby successively to retract pins (39) of thepin blocks (38) from the loop portions (101, 102) at the pin retractionstations (44, 45), (f) advancement track pin block biasing means (48,53) to bias the pin blocks (38) in each of the pin block advancementtracks (32, 33) into abutting engagement with each other, and (g) adrive mechanism (67) at a drive station in each of the advancementtracks (32, 33) to engage in turn each pin block (38) advanced theretounder the bias of the biasing means (48, 53) to drive the engaged pinblock (38) and all the pin blocks (38) in the advancement track (32, 33)between the drive station and the pin retraction station (44, 45) alongthe pin advancement track (32, 33) in the direction of the pinretraction station (44, 45) against the action of the biasing means (48,53) to bring a pin block (38) into the pin retraction station (44, 45)and to permit all pin blocks (38) in the track (32, 33) between thedrive station and the pin insertion station (40, 41) to advance in theadvancement track (32, 33) under the bias of the biasing means (48, 53)to bring a pin block (38) out of the pin insertion station (40, 41) andinto the pin block advancement track (32, 33) and to advance a pin block(38) into the drive station.
 2. A mechanism according to claim 1wherein:(a) the drive station in each of the advancement tracks (32, 33)is located at a position along the track intermediate the pin insertionstation (40, 41) and the pin retraction station (44, 45) and (b) theadvancement track pin block biasing means (48, 53) comprises:(i)forwardly acting biasing means (48) located at the pin insertion station(40, 41) in each advancement track (32, 33) to bias the pin blocks (38)between the pin insertion station (40, 41) and the drive station in thedirection of the drive station and into abutment with each other and(ii) rearwardly acting biasing means (53) located at the pin retractionstation (44, 45) to bias the pin blocks (38) between the drive stationand the pin retraction station (44, 45) in the direction of the drivestation and into abutment with each other.
 3. A mechanism according toclaim 2 wherein:(a) the drive mechanism (67) at the drive station ofeach pin-block advancement track (32, 33) comprises a drive pinion (69)located at the drive station and provided with equi-spaced peripheralteeth (70) and (b) each pin block (38) carries a tooth element (68)which is engagable at the drive station by a peripheral tooth (70) onthe pinion (69) for advancement of the pin block (38) along the pinblock advancement track (32, 33) upon rotary movement of the pinion(69).
 4. A mechanism according to claim 3 wherein:(a) each pin insertionstation (40, 41) includes a pin block insertion guide track (42)extending between an exit end of the pin block return track (34, 35) andan entry end of the pin block advancement track (32, 33) and (b) the pinblock insertion means (43) provides for displacing a pin block (38) at apin block delivery position in the pin block insertion track (42) at theexit end of the pin block return track (34, 35) to a pin insertionposition in the pin block insertion track (42) at the entry end of thepin block advancement track (32, 33) to insert the pin (39) of the pinblock (38) in the yarn loop portion at the station (40, 41) and forentry of the pin block (38) into the pin block advancement track (32,33).
 5. A mechanism according to claim 4 wherein:(a) each pin retractionstation (44, 45) extends between an exit end of the pin blockadvancement track (32, 33) and an entry end of the pin block returntrack (34, 35) and (b) the pin block retraction means (47) provides fordisplacing a pin block (38) at a pin block retraction position in thepin retraction station (44, 45) at the exit end of the pin blockadvancement track (32, 33) to retract the pin (39) of the pin block (38)from the yarn loop portion and to deliver the pin block (38) to a pinblock return position in the pin retraction station (44, 45) at theentry end of the pin block return track (34, 35) for entry into the pinblock return track (34, 35).
 6. A mechanism according to claim 4 whereinthe pin block advancement and return tracks (32, 33; 34, 35) arearranged to provide for horizontal movement of the pin blocks (38) andwherein the pin block insertion guide tracks (42) and the pin blockretraction means (47) are arranged to provide for movement of the pinblocks (38) vertically during insertion of pins (39) of the pin blocks(38) into the loop portions of the yarn structure being formed andduring retraction of the pins (39) of the pin blocks (38) at the pinretraction stations (44, 45).
 7. A mechanism according to claim 5wherein a return track pin-block biasing means (60) is provided at theentry end of the pin block return track (34, 35) to bias the pin block(38) at the pin block return position and all the pin blocks (38) in thepin block return track (34, 35) into abutting relationship for movementin the return track (34, 35) in the direction of the pin insertionstation (40, 41).
 8. A mechanism according to claim 7 wherein each pinblock (38) arriving at the exit end of the return track (34, 35) isdelivered to the pin block delivery position in the pin insertionstation (40, 41) under the action of the return track pin-block biasingmeans (60).
 9. A mechanism according to claim 1 wherein:(a) the firstpin block return track (34) is arranged parallel to and above the firstpin block advancement track (32), (b) the second pin block return track(35) is arranged parallel to and above the second pin block advancementtrack (33), and (c) the pin block retraction means (47) at each pinretraction station (44, 45) comprises a lifting device (47) whichengages the pin block (38) at the pin block retraction position andlifts it to the pin block return position.
 10. A mechanism according toclaim 9 wherein the lifting device (47) comprises a displaceable membercarrying retractable support means (471, 472) which ride over the pinblock (38) in a downward excursion of the lifting device (47) and engageunder the pin block (38) or a part or parts thereof to support the pinblock (38) during a return excursion of the lifting device (47), wherebythe pin block is lifted to the pin block return position.
 11. Amechanism according to claim 10 wherein the displaceable member is adisplaceable arm and wherein the retractable support means (471, 472)takes the form of one or more spring biased pawls.
 12. A machine forforming a multi-axial yarn structure comprising:(a) loop holdingmechanism (31) including a plurality of pin blocks (38) each of whichcarries a loop engaging pin (39), first and second pin block advancementtracks (32, 33) in which the pin blocks (38) are advanced from first andsecond pin insertion stations (40, 41) to first and second pinretraction stations (44, 45) spaced from the first and second pininsertion stations (40, 41) in the direction in which the formedmulti-axial yarn structure is to be advanced, first and second pin blockreturn tracks (34, 35) in which pin blocks (38) are returned from thefirst and second pin retraction stations (44, 45) to the first andsecond pin insertion stations (40, 41), first and second pin-blockinsertion means (43) at the first and second pin insertion stations (40,41) successively to transfer pin blocks (38) from the return tracks (34,35) to the advancement tracks (32, 33) for insertion of pins (39) of thepin blocks (38) in loop portions (101, 102) successively formed at thepin insertion stations (40, 41), first and second pin-block retractionmeans (47) at the first and second pin retraction stations (44, 45) totransfer the pin blocks (38) from the first and second advancementtracks (32, 33) to the first and second return tracks (34, 35) therebysuccessively to retract pins (39) of the pin blocks (38) from the loopportions (101, 102) at the pin retraction stations(44, 45), advancementtrack pin block biasing means (48, 53) to bias the pin blocks (38) ineach of the pin block advancement tracks (32, 33) into abuttingengagement with each other, and a drive mechanism (67) at a drivestation in each of the advancement tracks (32, 33) to engage in turneach pin block (38) advanced thereto under the bias of the biasing means(48, 53) to drive the engaged pin block (38) and all the pin blocks (38)in the advancement track (32, 33) between the drive station and the pinretraction station (44, 45) along the pin advancement track (32, 33) inthe direction of the pin retraction station (44, 45) against the actionof the biasing means (48, 53) to bring a pin block (38) into the pinretraction station (44, 45) and to permit all pin blocks (38) in thetrack (32, 33) between the drive station and the pin insertion station(40, 41) to advance in the advancement track (32, 33) under the bias ofthe biasing means (48, 53) to bring a pin block (38) out of the pininsertion station (40, 41) and into the pin block advancement track (32,33) and to advance a pin block (38) into the drive station, (b) warpyarn supply means (16) for supplying in a warp feed direction (F) warpyarns in the form of a warp sheet (17) and (c) a yarn transfer device(18) which subjects the warp yarns to successive bias yarn forming stepsin which each yarn is caused to move in a succession of lateral transfersteps in a first weft direction from a first bias yarn reversal positionto a second bias yarn reversal position and then to move in a successionof return lateral transfer steps in the opposite direction form thesecond bias yarn reversal position to the first bias yarn reversalposition thereby to form a non-woven bias yarn assembly comprising twosuperposed non-woven bias yarn sub-assemblies in which(i) the bias yarns(11) of one sub-assembly are inclined to the bias yarns (12) of theother sub-assembly, and (ii) the bias yarns (11, 12) are inclined to thewarp feed direction and wherein the loop holding mechanism (31) and theyarn transfer device (18) are so disposed that the bias yarns (11, 12)at each bias yarn reversal position in proceeding from a transfer stepin one direction to a transfer step in the opposite direction form biasyarn loop portions (101, 102) at the first and second edges of thestructure being formed.
 13. A mechanism according to claim 12wherein:(a) the drive station in each of the advancement tracks (32, 33)is located at a position along the track intermediate the pin insertionstation (40, 41) and the pin retraction station (34, 45) and (b) theadvancement track pin block biasing means (48, 53) comprises:(i)forwardly acting biasing means (48) located at the pin insertion station(40, 41) in each advancement track (32, 33) to bias the pin blocks (38)between the pin insertion station (40, 41) and the drive station in thedirection of the drive station and into abutment with each other and(ii) rearwardly acting biasing means (53) located at the pin retractionstation (44, 45) to bias the pin blocks (38) between the drive stationand the pin retraction station (44, 45) in the direction of the drivestation and into abutment with each other.
 14. A mechanism according toclaim 13 wherein:(a) the drive mechanism (67) at the drive station ofeach pin-block advancement track (32, 33) comprises a drive pinion (69)located at the drive station and provided with equi-spaced peripheralteeth (70) and (b) each pin block (38) carries a tooth element (68)which is engagable at the drive station by a peripheral tooth (70) onthe pinion (69) for advancement of the pin block (38) along the pinblock advancement track (32, 33) upon rotary movement of the pinion(69).
 15. A mechanism according to claim 14 wherein:(a) each pininsertion station (40, 41) includes a pin block insertion guide track(42) extending between an exit end of the pin block return track (34,35) and an entry end of the pin block advancement track (32, 33) and (b)the pin block insertion means (43) provides for displacing a pin block(38) at a pin block delivery position in the pin block insertion track(42) at the exit end of the pin block return track (34, 35) to a pininsertion position in the pin block insertion track (42) at the entryend of the pin block advancement track (32, 33) to insert the pin (38)of the pin block (38) in the yarn loop portion at the station (40, 41)and for entry of the pin block (38) into the pin block advancement track(32, 33).
 16. A mechanism according to claim 15 wherein:(a) each pinretraction station (44, 45) extends between an exit end of the pin blockadvancement track (32, 33) and an entry end of the pin block returntrack (34, 35) and (b) the pin block retraction means (47) provides fordisplacing a pin block (38) at a pin block retraction position in thepin retraction station (44, 45) at the exit end of the pin blockadvancement track (32, 33) to retract the pin (39) of the pin block (38)from the yarn loop portion and to deliver the pin block (38) to a pinblock return position in the pin retraction station (44, 45) at theentry end of the pin block return track (34, 35) for entry into the pinblock return track (34, 35).
 17. A mechanism according to claim 15wherein the pin block advancement and return tracks (32, 33; 34, 35) arearranged to provide for horizontal movement of the pin blocks (38) andwherein the pin block insertion guide tracks (42) and the pin blockretraction means (47) are arranged to provide for movement of the pinblocks (38) vertically during insertion of pins (39) of the pin blocks(38) into the loop portions of the yarn structure being formed andduring retraction of the pins (39) of the pin blocks (38) at the pinretraction stations (44, 45).
 18. A mechanism according to claim 16wherein a return track pin-block biasing means (60) is provided at theentry end of the pin block return track (34, 35) to bias the pin block(38) at the pin block return position and all the pin blocks (38) in thepin block return track (34, 35) into abutting relationship for movementin the return track (34, 35) in the direction of the pin insertionstation (40, 41).
 19. A mechanism according to claim 18 wherein each pinblock (38) arriving at the exit end of the return track (34, 35) isdelivered to the pin block delivery position in the pin insertionstation (40, 41) under the action of the return track pin-block biasingmeans (60).
 20. A mechanism according to claim 12 wherein:(a) the firstpin block return track (34) is arranged parallel to and above the firstpin block advancement track (32), (b) the second pin block return track(35) is arranged parallel to and above the second pin block advancementtrack (33), and (c) the pin block retraction means (47) at each pinretraction station (44, 45) comprises a lifting device (47) whichengages the pin block (38) at te pin block retraction position and liftsit to the pin block return position.
 21. A mechanism according to claim20 wherein the lifting device (47) comprises a displaceable membercarrying retractable support means (471, 472) which ride over the pinblock (38) in a downward excursion of the lifting device (47) and engageunder the pin block (38) or a part or parts thereof to support the pinblock (38) during a return excursion of the lifting device (47), wherebythe pin block is lifted to the pin block return position.
 22. Amechanism according to claim 21 wherein the displaceable member is adisplaceable arm and wherein the retractable support means (471, 472)takes the form of one or more spring biased pawls.